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Tokamak discharges using the expanded boundary divertor in the DIII-D device exhibit H-mode confinement. With neutral-beam power up to 6 MW, energy confinement remains comparable to the Ohmic value at a plasma current of 1 MA. Confinement is also independent of plasma density and toroidal field. Confinement increases with plasma current, but the exact functional dependence is, as yet, uncertain. These results show that the H mode can be achieved in a reactor-compatible open divertor configuration.

The first observation of $H$-mode confinement with electron heating as the sole auxiliary heating method has been made in divertor discharges in the DIII-D tokamak. These discharges exhibit the usual characteristics of the $H$ mode, including improved confinement of particles and energy, when electron cyclotron heating is added at a power level above 0.7 MW. The $H$-mode transition is accompanied by the development of an electron temperature pedestal of 0.25 keV and a dramatic steepening of the density gradient near the separatrix.